Charge pump regulator and method of producing a regulated voltage

ABSTRACT

A charge pump regulator has a charge pump to establish a charge path and a discharge path alternately, so as to produce a regulated voltage on an output terminal. The charge pump has at least a current control element on the charge path or the discharge path to control the current flowing therethrough according to an output-dependent feedback signal.

RELATED APPLICATIONS

This application is a Divisional patent application of co-pendingapplication Ser. No. 12/068,040, filed on 1 Feb. 2008. The entiredisclosure of the prior application Ser. No. 12/068,040, from which anoath or declaration is supplied, is considered a part of the disclosureof the accompanying Divisional application and is hereby incorporated byreference.

FIELD OF THE INVENTION

The present invention is related generally to a charge pump regulatorand, more particularly, to a high current charge pump regulator.

BACKGROUND OF THE INVENTION

As described in U.S. Pat. No. 6,411,531 to Nork et al., a pulsefrequency modulation (PFM) charge pump regulator comprises aswitch-capacitor network as a charge pump, in which switches areswitched with a modulated switching frequency according to anoutput-dependent feedback signal, to connect a capacitor to a powersupply or to an output terminal in order to charge and discharge thecapacitor, so as to produce a regulated voltage on the output terminal.Such circuit will cause large input ripple and thereby large supplyvoltage disturbance, and induce undesired low frequency noisesubsequently. It is not easy to process this low frequency noise, andvery large and expansive filter is required to filter out the lowfrequency noise.

U.S. Pat. No. 6,411,531 to Nork et al. also described another chargepump regulator which has switches in a charge pump switched with aconstant switching frequency, and a variable resistor inserted betweenthe charge pump and a ground terminal to be controlled by anoutput-dependent feedback signal to vary the resistance thereof. Thisvariable resistor limits the charge current to the capacitor in thecharge pump and reduces the input current ripple. However, the currentripple in the discharge phase is still large. Because of the smallerinput current in the charge phase, this circuit will cause smallersupply voltage disterbance. However, in the range of low frequency, forexample the switching frequency, the supply voltage disterbance causedby the input current ripple is still large. The large input currentripple also causes high frequency noise during the blank period whichhas all the switches in the charge pump open.

U.S. Pat. No. 6,411,531 to Nork et al. proposed an improved charge pumpregulator, which also operates with a constant switching frequency, buthas a variable resistor inserted between the power supply and the inputterminal of the charge pump. The resistance of the variable resistor isvaried according to an output-dependent feedback signal in order tocontrol the input current in each phase, so as to reduce the supplyvoltage disterbance that causes low frequency noise. However, the inputseries resistance is so increased, and thereby the power consumption isincreased, resulting in decreased efficiency of the charge pumpregulator.

Texas Instruments (TI) incorporated provides a product with serial no.TPS6500, which inserts a current source between the power supply and theinput terminal of the charge pump for providing a stable input current,so as to reduce the input ripple. However, this current source is stillan added element outside the charge pump.

SUMMARY OF THE INVENTION

One object of the present invention is to provide a low open loopresistance charge pump regulator.

Another object of the present invention is to provide a high efficiencycharge pump regulator.

Yet another object of the present invention is to provide a low ripple,high current charge pump regulator.

Still another object of the present invention is to provide a highcurrent-capacity charge pump regulator.

Yet still another object of the present invention is to provide a lowhigh-frequency noise charge pump regulator.

A further object of the present invention is to provide a smallchip-size charge pump regulator.

Still a further object of the present invention is to provide a methodof producing a regulated voltage.

A charge pump regulator according to the present invention comprises acharge pump connected between an input terminal and an output terminal,and a feedback loop to produce an output-dependent feedback signal forthe charge pump. The charge pump is operative to establish a charge pathand a discharge path alternately, and has at least a current controlelement on the charge path or the discharge path to control a currentflowing therethrough according to the output-dependent feedback signal.The output-dependent feedback signal may be produced from the outputterminal or a load-current.

The current control element controls the charge current or the dischargecurrent of a capacitor in the charge pump, thereby reducing the inputripple.

The current control element may replace the switch on the charge path orthe discharge path, thereby requiring no extra element, and thereforethe circuit needs smaller chip size.

No extra series resistance is added between the power supply and thecharge pump, or between the charge pump and ground terminal, therebyreducing the power consumption and improving the efficiencysubsequently.

The current control element is preferably a voltage-controlled powersource, such as voltage-controlled voltage source and voltage-controlledcurrent source.

Preferably, the charge pump regulator further comprises a widebandwidth, high slew rate buffer for driving the current control elementaccording to the output-dependent feedback signal, so as to reduce highfrequency noise.

The charge pump may be operative with a constant switching frequency, tothereby reduce the input ripple and the output ripple.

Preferably, multi-phase non-overlapping clocks are used for the chargepump to be switched between charge and discharge phases, so as to avoidshoot-through.

According to the present invention, a method of producing a regulatedvoltage comprises operating a charge pump for establishing a charge pathand a discharge path alternately, and producing an output-dependentfeedback signal to further produce a drive signal. The charge pump hasat least a current control element on the charge path or the dischargepath to be driven by the drive signal to control the current flowingtherethrough.

BRIEF DESCRIPTION OF DRAWINGS

These and other objects, features and advantages of the presentinvention will become apparent to those skilled in the art uponconsideration of the following description of the preferred embodimentsaccording to the present invention taken in conjunction with theaccompanying drawings, in which:

FIG. 1 shows a first embodiment according to the present invention;

FIG. 2 is a waveform diagram showing the drive signals used in thecircuit of FIG. 1;

FIG. 3 shows a second embodiment according to the present invention;

FIG. 4 shows a third embodiment according to the present invention;

FIG. 5 shows a fourth embodiment according to the present invention;

FIG. 6 is a waveform diagram showing the drive signals used in thecircuit of FIG. 5;

FIG. 7 shows a fifth embodiment according to the present invention;

FIG. 8 shows a sixth embodiment according to the present invention;

FIG. 9 is a waveform diagram showing the drive signals used in thecircuit of FIG. 8;

FIG. 10 shows a seventh embodiment according to the present invention;and

FIG. 11 shows an eighth embodiment according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a x1/x2 boost-type charge pump regulator, which comprises acharge pump 10 connected between an input terminal 12 and an outputterminal 14, an output capacitor 16 connected between the outputterminal 14 and a ground terminal GND, and other control circuits tocontrol the charge pump 10. A feedback loop comprises a resistor voltagedivider 18 to produce a proportional voltage V_(FB) from the outputterminal 14 by dividing the output voltage VOUT thereon, and anamplifier 20 to amplify the difference between the proportional voltageV_(FB) and a reference voltage V_(RFE) to produce an output-dependentfeedback signal opo. A buffer 22 is used to produce a drive signal gdaccording to the feedback signal opo. In this embodiment, the buffer 22comprises a current source 24 and a PMOS transistor 26 connected inseries between a power input VIN and a ground terminal GND, the gate ofthe PMOS transistor 26 is connected with the output-dependent feedbacksignal opo, and the drive signal gd is drawn from the source of the PMOStransistor 26. A clock generator 28 provides multi-phase non-overlappingclocks Φ1 and Φ2 for the charge pump 10 and a connector 30. The chargepump 10 comprises two switches 32 and 34, two current control elements36 and 38, and a capacitor 40. The switches 32 and 34 may be implementedwith PMOS transistor or NMOS transistor, and are switched by the clocksΦ1 and Φ2 respectively, only for establishing or disconnecting aconductive path. Each of the current control elements 36 and 38comprises a voltage-controlled voltage source (VCVS) or avoltage-controlled current source (VCCS) for controlling the currentflowing therethrough. In this embodiment, they are implemented with PMOStransistor operative in a linear region, and their drive signals g1 andg2 are provided by two connection units 42 and 44 in the connector 30respectively. The connection unit 42 comprises a transmission gate 46for connecting the drive signal gd to the gate of the PMOS transistor 36in the phase Φ1, and a switch 48 for pulling high the drive signal g1 toVOUT when not in the phase Φ1. Briefly, in the phase Φ1, the PMOStransistor 36 and the switch 34 are turned on so as to establish acharge path such that the power supply VIN connected to the inputterminal 12 may charge the capacitor 40; in the phase Φ2, the PMOStransistor 38 and the switch 32 are turned on so as to establish adischarge path such that the capacitor 40 will discharge to the outputterminal 14. As such, by alternately establishing the charge path andthe discharge path in the charge pump 10, the voltage VOUT on the outputterminal 14 is regulated.

FIG. 2 is a waveform diagram showing the drive signals g1 and g2, inwhich the multi-phase non-overlapping clocks Φ1 and Φ2 have anon-overlapping period 54 between the phases Φ1 and Φ2, so that theswitches 32 and 34 will not be turned on at the same time, and also thePMOS transistors 36 and 38 will not be turned on at the same time, toavoid shoot-through. In this embodiment, because of the PMOS transistor26 in the buffer 22, the drive signal gd will be higher than theoutput-dependent feedback signal opo by a gate-source voltage (V_(GSP))56 of the PMOS transistor 26. The current source 24 in the buffer 22 isused for preventing the source of the PMOS transistor 26 from connectingto the ground terminal GND. In the connector 30, when the clock Φ1 ishigh, the transmission gate 46 is turned on, the drive signal gd isconnected to the gate of the PMOS transistor 36, the drive signal g1 isthus equal to the drive signal gd, and the PMOS transistor 36 on thecharge path controls the charge current to the capacitor 40 according tothe drive signal gd. In this charge phase Φ1, the clock Φ2 is low, thetransmission gate 50 is turned off, thereby cutting off the pathconnecting the drive signal gd to the PMOS transistor 38, and the switch52 is turned on to remain the drive signal g2 at VOUT so as to turn offthe PMOS transistor 38. On the contrary, in the discharge phase Φ2, thetransmission gate 50 is turned on, thereby connecting the drive signalgd to the gate of the PMOS transistor 38 to control the dischargecurrent from the capacitor 40, the transmission gate 46 is turned off,thereby cutting off the path connecting the drive signal gd to the PMOStransistor 36, and the switch 48 is turned on to remain the drive signalg1 at VOUT so as to turn off the PMOS transistor 36.

FIG. 3 is an alternative embodiment, which is the same as the regulatorof FIG. 1 except that the output-dependent feedback signal opo isproduced from a load-current I_(OUT). The feedback loop in thisembodiment produces a proportional voltage V_(FB) from the load currentI_(OUT), and the proportional voltage V_(FB) is compared with areference V_(REF) by an amplifier 20 to produce the output-dependentfeedback signal opo. For producing the proportional voltage V_(FB), acurrent mirror 58 is used to mirror the load current I_(OUT) for a load60. In this embodiment, the load 60 is a light-emitting diode (LED) 60as an example, and the proportional voltage V_(FB) is drawn from theoutput terminal of the current mirror 58. The reference branch of thecurrent mirror 58 is connected to a current source 62 for preventing itfrom floating. Because the proportional voltage V_(FB) is the one acrossthe LED 60, it will be dependent on the load current I_(OUT). Forproducing the reference voltage V_(REF), a diode 64 and a current source66 are connected in series between the output terminal 14 and a groundterminal GND. The current source 66 prevents the diode 64 from floating.The reference voltage V_(REF) and the output voltage V_(OUT) have adifference therebetween, which is equal to the voltage across the diode64.

FIG. 4 is another embodiment for illustrating that the current controlelement 36 or 38 may be configured at different position on the samepath. As shown in FIG. 4, the current control element 38 and the switch32 are interchanged with their position on the same path, this chargepump regulator still operates in the same way as that of FIG. 1, and thedrive signals g1 and g2 also have the same waveforms as those shown inFIG. 2.

By changing the element configuration in the charge pump 10, there maybe obtained different types of charge pump regulators, for example thex1/x2 inverting boost-type charge pump regulator shown in FIG. 5. Inthis embodiment, because of the NMOS transistor 68 in the buffer 22, thedrive signal gd is lower than the output-dependent feedback signal opoby a gate-source voltage (V_(GSN)) of the NMOS transistor 68. Thecurrent control elements 70 and 72 are also implemented with NMOStransistors, and are driven by the drive signals g3 and g4 provided bythe connection units 42 and 44 respectively. The transmission gate 46connects the drive signal gd to the gate of the NMOS transistor 70 inthe charge phase Φ1, and the switch 74 pulls down the drive signal g3 toVOUT when not in this phase Φ1. The transmission gate 50 connects thedrive signal gd to the gate of the NMOS transistor 72 in the dischargephase Φ2, and the switch 76 pulls down the drive signal g4 to VOUT whennot in this phase Φ2. The switches 74 and 76 are also implemented withNMOS transistors. The switch 34 and the NMOS transistor 70 are used toestablish a charge path for the capacitor 40, and the switch 32 and theNMOS transistor 72 are used to establish a discharge path for thecapacitor 40. FIG. 6 is a waveform diagram showing the drive signals g3and g4 in the charge pump regulator of FIG. 5, in which the voltage 78represents the gate-source voltage V_(GSN) of the NMOS transistor 68. Inthe phase Φ1, the switch 34 is turned on by the clock Φ1, the switch 32is turned off by the clock Φ2, the NMOS transistor 70 is driven by thedrive signal gd, the transmission gate 50 cuts off the path connectingthe drive signal gd to the NMOS transistor 72, the drive signal g4prevents the NMOS transistor 72 from being turned on, the power supplyVIN connected to the input terminal 12 charges the capacitor 40, and theNMOS transistor 70 controls the charge current. On the contrary, in thephase Φ2, the switch 32 is turned on, the switch 34 is turned off, theNMOS transistor 72 is driven by the drive signal gd, the transmissiongate 46 cuts off the path connecting the drive signal gd to the NMOStransistor 70, the drive signal g3 prevents the NMOS transistor 70 frombeing turned on, the capacitor 40 discharges to the output terminal 14,and the NMOS transistor 72 controls the discharge current.

FIG. 7 shows a x1/x2 boost-type charge pump regulator, which is the sameas that of FIG. 1 except that its charge pump 10 employs fourvoltage-controlled power sources 80, 82, 84 and 86 to replace theswitches to establish and disconnect the charge path and the dischargepath. The connector 30 connects the drive signal gd to thevoltage-controlled power sources 80, 82, 84 and 86 according to theclocks Φ1 and Φ2, to establish the charge path and the discharge pathand control the charge current and the discharge current of thecapacitor 40.

FIG. 8 shows an alternative to the charge pump regulator of FIG. 7, inwhich the voltage-controlled power sources 80, 82 and 86 are implementedwith PMOS transistors, the voltage-controlled power source 84 isimplemented with NMOS transistor, and the feedback loop is the same asthat of FIG. 3 to produce the output-dependent feedback signal V_(FB)from the load current I_(OUT). However, for simultaneously producing thedrive signals g5, g8, g7 and g6 to control the PMOS transistors 80, 82and 86 and the NMOS transistor 84 respectively, the amplifier 20produces a pair of complementary output-dependent feedback signals opo−and opo+ for two units in the buffer 22 to produce two drive signals gd−and gd+ respectively, and four connection units in the connector 30 areused for establishing and cutting off the paths connecting the drivesignals gd− and gd+ to the NMOS transistor 84 and the PMOS transistors80, 82 and 86 respectively. The operations of the internal circuits ofthe buffer 22 and the connector 30 are the same as the above embodimentsand so will not be reiterated herein. The drive signals g5 to g8 in thischarge pump regulator are shown in FIG. 9, in which the drive signal gd+is higher than the output-dependent feedback signal opo+ by agate-source voltage (V_(GSP)) 56 of a PMOS transistor, and the drivesignal gd− is lower than the output-dependent feedback signal opo− by agate-source voltage (V_(GSN)) 78 of a NMOS transistor. In the chargephase Φ1, the drive signal gd+ is connected to the gate of the PMOStransistor 80, the drive signal gd− is connected to the gate of the NMOStransistor 84, the paths connecting the drive signal gd+ to the PMOStransistors 82 and 86 are cut off, the drive signals g7 and g8 arepulled high to VOUT to turn off the PMOS transistors 82 and 86, and thePMOS transistor 80 and the NMOS transistor 84 establish a charge pathsuch that the power supply VIN connected to the input terminal 12 willcharge the capacitor 40 and control the charge current. On the contrary,in the discharge phase Φ2, the drive signal gd+ controls the PMOStransistors 82 and 86, the PMOS transistor 80 and the NMOS transistor 84are turned off, and the PMOS transistor 80 and the NMOS transistor 84establish a discharge path such that the capacitor 40 will discharge tothe output terminal 14 and control the discharge current.

According to different demands, circuits with different pump ratios maybe employed for the charge pump 10. For example, FIG. 10 shows ax1/x⅔/x½/x⅓ boost-type charge pump regulator, which comprises eightvoltage-controlled voltage sources 80, 82, 84, 86, 90, 92, 94 and 96, aswitch 98, and two capacitors 40 and 88 configured to be a networkconnected between an input terminal 12 and an output terminal 14. Theother circuits of this regulator are the same as those of the aboveembodiments, and they are operated in the same way as the aboveembodiments and so will not be reiterated herein. Changing the elementconfiguration in the charge pump 10 will result in different types ofcharge pump regulators, for example a buck-type charge pump regulator isshown in FIG. 11, whose operations are referred to the above embodimentsand so will not be reiterated herein. Various types of charge pumps withvarious pump ratios are well known by those skilled in the art, and theycan follow the teaching of the present invention to change or modify thecircuits according to actual demands.

As shown in the above embodiments, both of the current control elementand the switch can be implemented with NMOS transistors, but the switchcan operate between two states, i.e. on and off, whereas the currentcontrol element can operate in a linear region and control the currentflowing therethrough according to the regulated voltage VOUT.Furthermore, controlling the charge current or the discharge current ofthe capacitor in the charge pump, the current control element can alsoreplace a conventional switch, and therefore a charge pump regulatoraccording to the present invention may have reduced input ripple andoutput ripple without adding any extra series resistors, resulting inhigher efficiency and smaller chip size. The lower open loop resistancealso improves the current-capacity of the charge pump regulator.Particularly, changing the element configuration in the charge pump mayimplement different types of charge pump regulators, such as boost-type,inverting boost-type and buck-type charge pump regulator, therebyincreasing the flexibility of circuit design.

While the present invention has been described in conjunction withpreferred embodiments thereof, it is evident that many alternatives,modifications and variations will be apparent to those skilled in theart. Accordingly, it is intended to embrace all such alternatives,modifications and variations that fall within the spirit and scopethereof as set forth in the appended claims.

1. A method of producing a regulated voltage, comprising the steps of:operating a charge pump for establishing a charge path and a dischargepath alternately, wherein the charge pump has at least a current controlelement on the charge path or the discharge path; producing aproportional current from a load current; producing a proportionalvoltage according to a variation of the proportional current; amplifyinga difference between the proportional voltage and a reference voltagefor producing an output-dependent feedback signal; deriving a drivesignal from the output-dependent feedback signal; and driving thecurrent control element with the drive signal for controlling a currentflowing therethrough.
 2. The method of claim 1, wherein the step ofdriving the current control element with the drive signal forcontrolling a current flowing therethrough comprises the step ofadjusting a voltage across the current control element.
 3. The method ofclaim 2, wherein the step of adjusting a voltage across the currentcontrol element comprises the step of operating a transistor in a linearregion for determining the current flowing through the current controlelement.
 4. The method of claim 1, wherein the step of deriving a drivesignal from the output-dependent feedback signal comprises the step ofcontrolling a transistor with the output-dependent feedback signal forproducing the drive signal.
 5. The method of claim 1, wherein the stepof deriving a drive signal from the output-dependent feedback signalcomprises the steps of: connecting the drive signal to the currentcontrol element in a first phase; and disconnecting the drive signalfrom the current control element in a second phase.
 6. The method ofclaim 5, further comprising the step of applying a voltage to turn offthe current control element in the second phase.